1. Field of the Invention
This invention generally relates to the field of reticle inspection. More particularly, the present invention relates to a method of integrated multi-pass inspection of a reticle.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a large number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that involves transferring a pattern from a reticle to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing (CMP), etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a single semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on reticles to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices such as ICs. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of semiconductor devices.
In general, existing methods for reticle inspection utilize one of two imaging modes to inspect a mask. The most common inspection mode known as reticle plane inspection (RPI) involves capturing high resolution transmitted and reflected images of a reticle and processing the two images together. The resolution is much higher than that of the wafer scanner used to print the reticle images to the wafer. The Teron™ platform designed, manufactured, and marketed by KLA-Tencor, Milpitas, Calif. is the industry standard inspection tool for RPI inspection modes. This type of inspection has the best performance for finding relatively small point defects. As optical proximity correction (OPC) gets more complex, it can be challenging to use this inspection mode to differentiate between primary features, where defect detection sensitivity needs to be high due to the criticality of the primary features, and assist features, where defect detection sensitivity can be lower due to the non-criticality of these features. It can also be challenging to use this inspection mode to separate non-wafer-printing nuisance defects on primary features from critical, wafer-printing defects due to the complex rules in geometry classification typically used in defect detection. In a die-to-die inspection, since database information is typically not used for defect detection, geometry classification can be even more difficult, which can make separating printing critical defects from non-printing nuisance defects challenging. Furthermore, this approach has difficulties finding diffuse and phase defects, which are becoming more common and important to catch.
Another inspection method called low numerical aperture (NA) inspection (LNI) involves a mode that emulates the wafer scanner optical conditions, capturing one image in transmitted light at a lower NA than RPI with illumination conditions that approximate the scanner's. Utilizing this method allows the system to differentiate between primary features with high sensitivity and assist features regardless of the reticle type or complexity of the underlying patterns on the reticle. It also enables estimating the printability impact of a defect on the wafer plane. Furthermore, LNI inspection mode readily detects diffuse and phase defects due to the optical conditions of the LNI mode. However, this mode has fundamentally lower resolution making it difficult to find relatively small point defects.
Another method for contamination inspection known as SL involves analyzing two images, RPI transmitted and reflected, to find defects that standout from the background pattern. This method can be challenged by more complex masks where the assist and optical proximity correction (OPC) patterns look substantially similar to the contamination that the defect detection algorithm is trying to detect.
Accordingly, it would be advantageous to develop methods and/or systems for reticle inspection that do not have one or more of the disadvantages described above.